In the wide field of manufacturing semiconductor elements such as LSIs, producing liquid crystal display surfaces of LCD panels, manufacturing circuit substrate for a thermal head, and like use, resist patterns have been formed on substrates for formation of fine elements or fine processing. In the formation of resist patterns, a so-called photolithography process has been employed which involves exposing by selectively irradiating a photosensitive resin composition with an actinic ray such as ultraviolet ray, deep ultraviolet ray, excimer laser, x-ray, or electron beams and developing the resin composition. In the photolithography process, negative or positive-working photosensitive resin compositions are used to form resist patterns. With the recent trend of higher integration of semiconductor devices, wiring and separation widths required in the manufacturing process of the semiconductor device are becoming finer, and, in order to keep up with this trend, exposure equipment employing a short-wavelength light source such as g-line, i-line, or excimer laser or phase shift masks are used in the exposure. However, with the lithography technique employing the conventional exposure, it is difficult to form resist patterns that are finer than the limit provided by the wavelength. On the other hand, exposure equipment for short-wavelength and equipment employing phase shift masks are expensive. Therefore, methods to effectively make resist patterns finer, which use conventionally known positive or negative-working photosensitive resin compositions and conventionally known pattern formation equipment without using the expensive equipment, have been intensively investigated, and are disclosed, for example, Japanese Patent Application Laid-Open Nos.5-241348, 6-250379, 10-73927, and 11-204399. The methods described in these publications involve following steps, that is, employing a conventional photosensitive composition, forming a pattern by conventional methods, forming a coating layer on the resist pattern formed, allowing an acid generated by heating and/or exposure to light of the resist or present in the resist to diffuse into the coating layer, crosslinking and curing the coating layer by the action of the acid which has diffused into the coating layer, removing the uncrosslinked coating layer to thicken the resist pattern, and, as a result, the intervals between the resist patterns are narrowed, and the separation size or hole aperture size of the resist patterns are reduced to make resist patterns finer and to effectively form resist patterns which are fine to a degree below the resolution limit.
In the methods of forming fine patterns mentioned above, a water-soluble photosensitive or non-photosensitive resin composition which can be crosslinked by an acid is used as a composition for forming a coating layer, and water or a mixed solvent with water and an organic solvent is used for development and removal of uncrosslinked coating layer. When water or a mixed solvent with water and an organic solvent is used as a developer and the coating layer is excessively insolubilized, there arise such problems that bridging may be formed in the resist pattern after development, development residues such as scum may be generated, and components containing hydrophobic groups in the water-soluble resin composition for coating layers may adhere as insolubles to the surface of wafer during the development, which result in pattern defect (see FIGS. 1 and 2). Although the bridging and scum may be prevented in some cases by applying existing approaches such as discharging a lot of developer comprising water or water and an organic solvent or by increasing the number of times of paddle development, it is difficult to control the reproducibility and uniformity of pattern dimensions made finer. Therefore, there has been required a improvement for higher yield, easier operation, and more stable process.
When a water-soluble resin composition which crosslinks by an acid to form an insolubilized layer is used as a material to form a coating layer, the acid concentration generated in the base resist pattern varies depending on the locations in cases where several patterns with different pattern dimensions are present in the base resist pattern, or patterns are configured sparsely and densely, or a certain arrangement of the pattern is present. This unevenness produces a variation in the crosslinking density in the coating layer, which lowers the dimensional controllability of the resultant pattern. Furthermore, when a solution such as a mixed solution of water and an organic solvent which shows a high solubility toward the coating layer is used as a developer, the dissolution rate varies in the different pattern arrangements, which results in reduced dimensional controllability of the resultant pattern. Since attempts to substantially avoid this problem requires slight changes in the design of the exposure pattern such as the pattern dimension and pattern arrangement of the base resist, this situation is in need of improvement in terms of the cost and easiness of manufacturing semiconductor devices.
Examples of the method of forming fine resist patterns mentioned above include use of water or aqueous TMAH (tetramethylammonium hydroxide) solution for development of a coating layer comprising a water-soluble resin composition as disclosed in Japanese Patent Application Laid-Open No.10-73927 and development of a coating layer comprising a water-soluble resin composition with a solution comprising water and an organic solvent, which has a high solubility to the composition, and rinsing the coating layer with a solution having a low solubility to the composition such as water as disclosed in Japanese Patent Application Laid-Open No.11-204399. Although the latter patent application describes the solution with a high solubility contains a surfactant, neither specific examples of the surfactant nor the effect of the surfactant are described. These conventional methods may result in development defect and pattern defect without enough dimensional controllability of the resultant fine resist pattern. Under the present circumstances, coating layers cannot be formed independent on the dimension and arrangement of the base resist pattern and without influencing the base resist pattern and the shrunk resist pattern, and the dimensional controllability of the resultant resist pattern cannot be significantly improved.
Furthermore, Japanese Patent Application Laid-Open No. 11-204399 describes that the developer contains a surfactant, but there are problems in such a case that air bubbles are formed when a developer is discharged onto a wafer in development, and all of the generated air bubbles do not disappear in the developer, which makes the development uneven and produces a pattern with low dimensional controllability. Therefore, a low-frothing surfactant or a surfactant which highly defoams even if it once froths up is required as a surfactant for use in a developer.
It is an object of the present invention to provide an surfactant aqueous solution for development of a coating layer which is free from the above-mentioned problems and a method of forming fine resist patterns which employs this surfactant aqueous solution.
Accordingly, the object of the present invention is to provide an surfactant aqueous solution for development of a coating layer, which can prevent formation of bridging caused by excessive crosslinking, generation of development residues such as scum, and reattachment of insolubles, and which does not influence the base resist pattern or the resist pattern made finer (or shrunk), and which works independent of the dimension and pattern arrangement of the base resist pattern, and which cannot cause uneven development attributable to froths of the developer, and which can improve the dimensional controllability of the pattern, in the method of forming a pattern where a trench pattern and a hole pattern can be effectively made finer to a degree below the resolution limit by forming a coating layer on a resist pattern and thickening the resist pattern, and a method of forming fine resist patterns which employs this surfactant aqueous solution